fix(qmd): honor XDG_CACHE_HOME for the setup-owned model files

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/lib/qmd.py

@@ -77,7 +77,7 @@ class Setup:
         self.base = self.home / '.my-ai-configuration'
         self.state_path = self.base / 'qmd.json'
         self.scripts = self.base / 'qmd'
-        self.models = self.home / '.cache' / 'qmd' / 'models'
+        self.models = Path(os.environ.get('XDG_CACHE_HOME') or self.home / '.cache') / 'qmd' / 'models'
 
     def say(self, text):
         if not self.summary: